You are right in the fact that there could be potential for capital appreciation. After all, bonds move inversely with interest rates and the longer the maturity, the more susceptible they are to movements. A small drop in rates can have a big impact on the longer end of bonds.
The only difficulty here is even if the Fed does cut rates the long end of the curve doesn't always follow immediately. As Warren said in the comments, if there is any fears of tariff related inflation or just inflation in general, long-term bonds could fall in price due to selling activity no matter which direction rates go.
Your methodology and idea here is sound. However, going all in one duration of bond, especially on the longer end of the curve, can be extremely risky from a fixed income perspective. If you're looking to add a mix of bonds into your portfolio, I'd be mixing the maturities as well. It could reduce your overall volatility and you could still stand to benefit if your thesis on the long-term works out.